The purposes of this research are the investigation of the biochemical and morphologic characteristics of developing central nervous system (CNS) cells in dispersed cell cultures, and the use of these cultures in conjunction with sensitive biochemical tests to assess the toxicity and mechanisms of action of nervous system active drugs. Among agents used to treat generalized tonicclonic seizures, extensive statistical analyses of the assay data have shown that phenytoin has the most severe effect on neuronal survival and carbamazepine has the least. Phenobarbital effects were of lesser magnitude, but were statistically equivalent to those of phenytoin except for assays of choline acetyltransferase (CAT) activity. Dose-response studies of CAT activity after phenytoin or phenobarbital exposure indicated a two-fold greater toxicity for phenytoin. With respect to agents used to treat absence seizures, valproic acid and diazepam produced slight to moderate neuronal loss, whereas ethosuximide exposure did not affect neuronal survival. However, exposure to each of these three drugs resulted in significant decrease in CAT activity and benzodiazepine receptor binding beyond levels to be expected from neuronal loss. Thus, cholinergic and benzodiazepine receptor systems were selectively affected by this class of drugs suggesting that these systems may be involved in the anticonvulsant action of these agents. Disproportionate reductions in Beta-alanine uptake in cultures exposed to valproic acid indicated that valproate also affects non-neuronal Gamma-amino butyric acid metabolism.